ValueError: Not a valid PEM pre boundary

this piece of code

key=RSA.importKey(open("receiver.pem","rb").read())

returns this error

ValueError: Not a valid PEM pre boundary

and

key=RSA.importKey(open("receiver.pem","r").read())

returns

ValueError: Not a valid PEM post boundary

The code worked fine when we used Pycrypto and Python 2.7, now i have shifted to Pycryptodome and Python 3.4.3(using 2to3). But now this code won't work. I can't even try anything because i can't even understand what it means.

To generate the .PEM file this code was used.

random_generator = Random.new().read
rsakey = RSA.generate(1024, random_generator)
f=open(email+'.pem','wb')
f.write(rsakey.exportKey("PEM"))
f.write(rsakey.publickey().exportKey("PEM"))
f.close()

This is what the contents of a .PEM file is like.

Solution

You are getting that error because of this function:

def decode(pem_data, passphrase=None):
    ...

    # Verify Pre-Encapsulation Boundary
    r = re.compile("\s*-----BEGIN (.*)-----\n")
    m = r.match(pem_data)
    if not m:
        raise ValueError("Not a valid PEM pre boundary")
    marker = m.group(1)

    # Verify Post-Encapsulation Boundary
    r = re.compile("-----END (.*)-----\s*$")
    m = r.search(pem_data)
    if not m or m.group(1) != marker:
        raise ValueError("Not a valid PEM post boundary")

Unfortunately, in non-multiline regular expressions, $ means "end of the string". This implies that PyCryptoDome expects the END boundary at the end of the string, and there are no ways to work around this problem.

You have three options:

split the two keys and import them separately;
fix PyCryptoDome;
switch back to PyCrypto.